Moore's Law, related to the scaling of electronic devices, postulates that the number of field effect transistors (FETs) in dense integrated circuits will double approximately every two years. While this prediction has held true for many years, dimensional limitations will likely make it impossible to keep up with this historical rate of growth.
Many alternative means of enhancing device performance are currently being explored. Some use novel materials such as carbon nanomaterials, metal dichalcogenides, and the like as channels for FET and alternative device architectures. Alternative device architectures may include, tunnel FET, micro-electro-mechanical switches, single electron transistors, molecular switches, etc. All of these proposed changes are aimed at emulating the switching properties of FETs at smaller size-scales. Research in these areas is evolving, though few have shown any promising solutions thus far. On the other hand, there have been some recent efforts in using the pre-silicon era triode devices in nanoscale format to enable ballistic transport of carrier in atmospheric condition from one contact to the other.
A traditional triode is an evacuated tube device having three elements: a cathode filament, a control grid, and an anode plate (just as the “di” in the name diode refers to two elements, filament and plate). While the device was the de-facto standard prior to widespread uses of the FET, the triode suffered from relatively high current consumption (as a result of the resistive heated filament. Additionally, switching speeds were limited to a fraction of what is often required by today's design requirements. Of course, perhaps one of the greatest limitations was size; having a footprint thousands of times larger than a comparable FET.
However, if a nano-structure could be fabricated to mimic the desirable features of the triode, many of the former limitations would be obviated. Some attempts to emulate the triode in a nano-form-factor have included contacts spaced in the range of 20-150 nm. That spacing dimension is much smaller than the mean free path of electrons in atmospheric condition. As a result, application of bias across the contact enables field emission of electron from anode that transports to cathode in a ballistic manner. Using appropriate gate structure, the field emission can be switched on/off, to mimic the same operation in a FET or a tube triode. Existence of ballistic transport (i.e., the highest possible mobility) in these nanoscale triodes, even at length scales of ˜100 nm, promises to have significant performance improvement over any of the existing FET configuration reported so far.
Unfortunately, performance in these nanoscale triode are currently limited because of (a) low field emission from the smaller aspect ratio structures being used, (b) high gate current (since field emissions from the cathode are diverted from anode to gate), and (c) thermal runaway when operated at higher current levels. Therefore, these triodes show limitation in scaling them down to the nanometer regime as needed for high performance applications.
As a result, there exists a need in the art for low power consumption nanoscale triode having sufficient field emissions and manageable heat generation properties.